This invention relates to a valve mechanism for an internal combustion engine of the type in which a semi-spherical recess is formed on a pivot member disposed on an engine main body and a spherical fitting portion to fit to the semi-spherical recess is disposed at the base end of a cam follower that is interposed between a cam and an intake valve or an exhaust valve.
In a conventional valve mechanism of the kind described above, the center of curvature C1' of the semi-spherical recess 10' is disposed on its center line together with the center of curvature C2' of the spherical fitting portion 12'. The radius of curvature R1' of the semi-spherical recess 10' is set to be greater than the radius of curvature R2' of the spherical fitting portion 12', as shown in FIG. 4 of the accompanying drawings.
In accordance with the conventional technique shown in FIG. 4, the spherical fitting portion 12' and the semi-spherical recess 10' come into contact with each other at the bottom of the semi-spherical recess 10'. Therefore, during the operation of the valve mechanism, lateral movement of the spherical fitting portion 12' is repeated in accordance with the rocking of a cam follower and in an extreme case, the spherical fitting portion 12' can override the rim of the semi-spherical recess 10'. Therefore, the contact position between the spherical fitting portion 12' and the semi-spherical recess 10' is unstable. Additionally, the noise of their contact is loud and irritating.